1. Field of the Invention
The present invention relates to an improved rotary driling tool having great efficiency in cleaning the cutting face.
2. Description of the Prior Art
Rotary drilling tools are already known comprising a body having a first end which is connected to a rotary drive means and a second end, which delimits the cutting face and which comprises a plurality of working zones distributed about the axis of the drilling bit, while being separated by radial zones for removal of the spoil or cuttings; these zones communicating at their periphery with an annular space surrounding a first end of the drilling bit, in front of the cutting face.
In some tools of this type, described for example in the published British patent application No. GB-A-2 047 308, each of the working zones of the drilling bit comprises a plurality of ribs, or segments, of elongate shape each of which has a working face carrying a cutting element advantageously formed by sintered diamond.
The assembly of the working faces of the same zone form a line for working the ground. Each working zone comprises a row of irrigation nozzles opening along the radius of the cutting face, in front of the working line of this zone, if we consider the direction of rotation thereof on the cutting face. These nozzles create irrigation jets flowing in a direction substantially parallel to the working faces of the ribs, at a certain distance from the working faces.
It is also known to improve the cleaning of the cutting face and removal of the spoil or cuttings by positioning nozzles whose jets are slanted with respect to the cutting face and therefore strike the wall at an angle of incidence different from 90.degree..
The prior art may be illustrated by the U.S. Pat. Nos. 3,645,346, 3,838,742 and 4,323,130.
A drawback of the prior art resides in the fact that the distribution presently adopted for these jets does not promote good cleaning of the central part of the tool, which limits the advancing rate performance of the tool and increases the wear thereof.
The purpose of the present invention is to provide an improvement to drilling tools to increase their performances by a more efficient removal of spoil from the cutting face and more particularly in the central part, or central zone, of the tool.